<template>
  <div>
    <ul class="list">
      <li
        class="item"
        v-for="item in letters"
        :key="item"
        @click="handleLetterClick"
        @touchstart.prevent="handleTouchStart"
        :ref="item"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
      >{{item}}</li>
    </ul>
  </div>
</template>

<script>
export default {
  name: "CityAlphabet",
  props:{
    cities: Object
  },
  data() {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    };
  },
  computed: {
    letters() {
      const letters = [];
      for (let i in this.cities) {
        letters.push(i);
      }
      return letters;
    }
  },
  updated() {
    this.startY = this.$refs["A"][0].offsetTop;
  },
  methods: {
    handleLetterClick(e) {
      this.$emit("change", e.target.innerHTML);
    },
    handleTouchStart() {
      this.touchStatus = true;
    },
    handleTouchMove(e) {
      if (this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.time);
        }
        this.timer = setTimeout(() => {
          const touchY = e.touches[0].clientY - 79;
          const index = Math.floor(touchY - this.startY) / 20;
          if (index >= 0 && index < this.letters.length) {
            this.$emit("change", this.letters[index]);
          }
        }, 16);
      }
    },
    handleTouchEnd() {
      this.touchStatus = false;
    }
  }
};
</script>

<style lang="scss" scoped>
  @import "~styles/varibles.styl";
  .list{
    position :absolute;
    right :0;
    top :1.58rem;
    bottom :0;
    display: flex;
    width: .4rem;
    flex-direction: column;
    justify-content: center;
    .item{
      text-align: center;
      line-height: 0.4rem;
      color: $bgColor;
    }
  }
    
    
      
</style>
